The present invention relates to a method for regulation of currents during phases of stoppage, in electromagnetic actuators, for actuation of intake and exhaust valves in internal-combustion engines.
As is known, propulsion units are currently at an experimental stage, in which the actuation of the intake and exhaust valves is controlled by means of use of actuators of an electromagnetic type, which replace the purely mechanical distribution systems (cam shafts).
In particular, these actuators comprise a pair of electromagnets disposed on opposite sides of a mobile ferromagnetic element, which is connected to a respective intake or exhaust valve, and is maintained in a position of rest by means of resilient elements (for example a spring and/or a torsion bar). The mobile ferromagnetic element is actuated by means of application of a force generated by the electromagnets, such that it is made to abut alternately one or the other of the electromagnets itself, so as to move the corresponding valve between the positions of closure and maximum opening, according to required times and paths. By this means, it is possible to actuate the valves according to optimum raising conditions in all operative conditions of the engine, thus improving substantially the overall performance.
In addition, during phases of stoppage, it is necessary to retain the valves alternately in the position of closure or of maximum opening. For this purpose, it is known to supply to the electromagnets maintenance currents with a pre-determined intensity, which is lower than the intensity of the currents distributed during the phases of movement of the valves (phases of flight), but is sufficient to prevent any disturbances, such as unforeseen variations of pressure, dispersion current or drift caused by wear of the components, from giving rise to displacements of the valves themselves from the required position.
However, by this means, there is a high absorption of electrical power which does not make it possible to obtain optimum performance levels. In fact, the maintenance currents must guarantee that the force exerted on the mobile element by the electromagnets is greater than the forces of disturbance which can intervene. Since the intensity of these currents is set during calibration, and cannot be modified except by means of intervention by specialised personnel, it is necessary to provide a margin of safety. Consequently, the maintenance currents distributed are far greater than those which are actually necessary, moment by moment, in order to maintain the valves in the respective required positions. Since, in addition, the duration of the phases of stoppage is far greater than the duration of the phases of flight, in which the valves are displaced between the respective positions of closure and maximum opening, the overall performance of the engine is disadvantageously reduced.
The object of the present invention is to provide a method for regulation of currents during phases of stoppage, which makes it possible to overcome the disadvantages described, and which, in particular, makes if possible to reduce the overall consumption of electrical power.
According to the present invention, a method is provided for regulation of currents during phases of stoppage in electromagnetic actuators for actuation of intake and exhaust valves in internal combustion engines, in which an actuator is connected to a respective intake or exhaust valve which has a position, and comprises a mobile unit which is actuated magnetically in order to control the movement of the said valve, a sensor which supplies a position signal representative of a present position of the said mobile unit, and a first and a second electromagnet, which are disposed on opposite sides of the said mobile unit, and receive respectively a first and a second current; the said mobile unit being disposed in a position of stoppage during phases of stoppage; the said position of stoppage corresponding alternately to a first position of end of travel, in which the said mobile unit abuts the said first electromagnet, and to a second position of end of travel, in which the said mobile unit is disposed such as to abut the said second electromagnet; the method being characterised in that it comprises the phases of:
a) setting at least one current out of the said first and second currents to an initial maintenance value, when the said valve is in the said position of stoppage;
b) checking that the said valve remains in the said position of stoppage for a pre-determined interval of time; and
c) decrementing the said at least one current, if the said valve has remained in the said position of stoppage for the said pre-determined interval of time.